Current decay control in switched reluctance motor

Claim 1

A circuit for controlling residual current decay in a single or polyphase SRM comprising: sensing means for sensing the position of a rotor of the motor; switch means for directing current flow into a phase winding of the motor when the phase is active and for recovering or dissipating energy in the winding when the phase is inactive, the switch means comprising a first set of switches and a second set of switches, said sets of switches being on respective sides of the phase winding with one set of switches being activated when the phase is active, and deactivated when the phase is inactive; signal generating means providing an operating signal to the switch means to control current flow and recovery or dissipation, the signal generating means including a PWM signal generator whose output signal pulse width and frequency are a function of the SRM's operating characteristics, the second set of switches being modulated by operating signals from the signal generating means whereby operation of the second set of switches is controlled as a function of the signal characteristics of the operating signal; a capacitor connected in series with the phase winding and charged by the current in the phase winding when the phase becomes inactive thereby to recover a portion of the energy; and control means responsive to the sensing means for controlling the signal generating means for the signal generating means to provide operating signals having operating characteristics which differ when a phase is active and when it is not, thereby to facilitate energy recovery or dissipation when the phase becomes inactive, the control means effecting both frequency and/or duty cycle of the operating signals to control the rate of decay of the current and consequently motor noise, the control means being responsive to inputs from the sensing means when the phase becomes inactive to reverse the pulse width of the PWM operating signals produced by the signal generating means from those which are produced when the phase is active.

Claim 17

A method for controlling tail current decay in a phase winding of a single or polyphase SRM, current and voltage being applied to the phase winding during each interval when the phase is active with the voltage and current being cut-off from the phase winding when the phase becomes inactive, the energy in the phase winding when the phase becomes inactive having to be recovered or dissipated under a zero volt condition, the method comprising: switching the phase winding into a circuit including a bus capacitor which stores current to recover energy while the phase is inactive, switching the phase winding into the circuit including switching respective first and second sets of switches, one set of switches being connected to one side of the phase winding and the other set of switches being connected on the other side thereof; alternately switching the winding into an energy dissipation circuit to dissipate a portion of the energy, the winding being switched back and forth between the respective circuits over a plurality of intervals so to decay the current in a controlled manner; sensing the rotor position of the motor while the phase is inactive; generating and supplying an operating signal to the switches to effect switching of the phase winding between the bus capacitor circuit and the energy dissipation circuit; and, modulating the operation of one of the sets of switches with the operating signals whereby one set of switches remains closed throughout the interval when the phase is inactive and the other set of switches is switched back and forth between open and closed at a modulating frequency determined by the signal characteristics of the operating signal for the tail current to be hard chopped during each interval when both sets of switches are closed, and soft chopped during each interval when the one set of switches is closed and the other set of switches is open thereby to provide a zero volt current decay which is controlled so as to minimize motor noise.

Claim 18

A method for controlling tail current decay in a phase winding of a single or polyphase SRM, current and voltage being applied to the phase winding during each interval when the phase is active with the voltage and current being cut-off from the phase winding when the phase becomes inactive, the energy in the phase winding when the phase becomes inactive having to be recovered or dissipated under a zero volt condition, the method comprising: switching the phase winding into a circuit including a bus capacitor which stores current to recover energy while the phase is inactive, switching the phase winding into the circuit including switching respective first and second sets of switches, one set of switches being connected to one side of the phase winding and the other set of switches being connected on the other side thereof; alternately switching the winding into an energy dissipation circuit to dissipate a portion of the energy, the winding being switched back and forth between the respective circuits over a plurality of intervals so to decay the current in a controlled manner; sensing the rotor position of the motor while the phase is inactive; generating and supplying an operating signal to the switches to effect switching of the phase winding between the bus capacitor circuit and the energy dissipation circuit; and, modulating the operation of one of the sets of switches with the operating signals whereby one set of switches remains closed throughout the interval when the phase is inactive and the other set of switches is switched back and forth between open and closed at a modulating frequency determined by the signal characteristics of the operating signal for the tail current to be hard chopped during each interval when both sets of switches are closed, and soft chopped during each interval when the one set of switches is closed and the other set of switches is open thereby to provide a zero volt current decay which is controlled so as to minimize motor noise.

Claim 23

A method of decaying the residual current in a winding of a single or polyphase SRM, current being supplied to the winding when the phase is active and the residual current being the current remaining in the winding when the phase become inactive, the method comprising: switching the winding between a first circuit which is an energy recovery circuit to recover a portion of the energy represented by the residual current and a second circuit which is an energy dissipation circuit which dissipates a portion of the energy represented by the residual current; controlling the switching of the winding between the energy recovery and energy dissipation circuits in a controlled manner by which the residual current is decayed to zero so as to cause minimal ringing in the motor and thereby reduce motor noise, controlling switching of the winding including switching the winding between the circuits over a plurality of intervals with the winding being switched into one circuit for a portion of each interval and into the other circuit the remainder of the interval, both the duration of each interval and the portion thereof in which the winding is switched into one circuit or the other being variable in a predetermined manner.

Claim 24

A method of decaying the residual current in a winding of a single or polyphase SRM, current being supplied to the winding when the phase is active and the residual current being the current remaining in the winding when the phase become inactive, the method comprising: switching the winding between a first circuit which is an energy recovery circuit to recover a portion of the energy represented by the residual current and a second circuit which is an energy dissipation circuit which dissipates a portion of the energy represented by the residual current; controlling the switching of the winding between the energy recovery and energy dissipation circuits in a controlled manner by which the residual current is decayed to zero so as to cause minimal ringing in the motor and thereby reduce motor noise, controlling switching of the winding including switching the winding between the circuits over a plurality of intervals with the winding being switched into one circuit for a portion of each interval and into the other circuit the remainder of the interval, both the duration of each interval and the portion thereof in which the winding is switched into one circuit or the other being variable in a predetermined manner.